1. Field of the Invention
The present invention relates to lasers and particularly to a flashpumped 2 micron solid state laser with high slope efficiency at or near room temperature.
2. Description of the Prior Art
Development of room temperature solid state lasers in the two micron spectral range has received renewed attention recently because of potential applications in medicine and optical communications. Q-switched 2 micron lasers are of particular importance since they can provide efficient pump lines for tunable parametric oscillators covering the entire 2-12 micron region.
Demonstrations of laser action around 2.0 microns, using the .sup.5 I.sub.7 -.sup.5 I.sub.8 transition of Ho.sup.3+, as well as the .sup.3 F.sub.4 -.sup.3 H.sub.6 transition of Tm.sup.3+, appeared among the early reports on rare earth ion lasers. One difficulty with both of these 2.0 micron transitions is due to the fact that the terminal laser level is only separated from the ground state by a Stark splitting on the order of 10.sup.2 -10.sup.3 cm.sup.-1. Thus, the early laser demonstrations were performed at cryogenic temperatures in order to reduce the Boltzmann population of the lower laser level.
Efficient flashlamp pumping of the Tm.sup.3+ and Ho.sup.3+ was accomplished by the addition of a sensitizer ion, such as Cr.sup.3+ or Er.sup.3+. A number of concentration and/or temperature-dependent energy transfer processes, both beneficial and detrimental, occur in these multiply-doped laser materials. Knowledge of these effects has been utilized previously in order to obtain efficient flashlamp-pumped room temperature (FPRT) 2 micron laser operation from Ho.sup.3+.
A recent study has been reported on a cryogenic 2.01 micron Cr:Tm:YAG laser that has a maximum slope efficiency of 0.48% with a threshold of 25 J at 130 K, and thresholds have been projected on the order of 100 J for flashlamp pumped room temperature operation. This previous study has been reported in an article entitled "Thulium YAG laser operation at 2.01 .mu.m" by M. E. Storm, D. J. Gettemy, N. P. Barnes, P. L. Cross and M. P. Kokta, published in Appl. Opt., Vol. 28, No.3, pp. 408-409 (1 Feb.1989). However, this recent study on the cryogenic 2.01 micron Cr:Tm:YAG laser has suggested that achievement of similar flashpumped room temperature efficiencies for Tm.sup.3+ may not be possible.